Miniaturized devices, such as actuators, micro-optics, micro-fluidics, tunable electronics (filters), scanning probe microscope tips, micropower generators, and sensors (for example, temperature, pressure, acceleration, flow, radiation, chemical species etc.) sometimes include micromechanical structures formed from semiconductor materials. The micromechanical structures can be, for example, a membrane, cantilever beam, or tethered proof mass, etc., which is designed to be perturbed by external stimuli when used as a sensor, or to produce a motion when used as an actuator. Typically, the micromechanical structures are micromachined by an etching process. In some instances, a film of polycrystalline material is deposited over the micromechanical structure to provide the micromechanical structure with additional properties. For example, the film may have piezoresistive, piezoelectric, etc., properties. A drawback of polycrystalline films is that it is difficult to produce polycrystalline films that have constistent or uniform properties. In addition, some desirable functional properties are not provided by polycrystalline films. Furthermore, polycrystalline films are usually less stable at high temperatures and corrosive environments which restricts operation of devices including these films to lower temperatures and less corrosive environments.
The present invention provides a micromechanical device with highly reproducible properties and improved functionality that is capable of operating at higher temperatures and in more corrosive environments than previous devices. The micromechanical device includes a single crystal micromachined micromechanical structure. At least a portion of the micromechanical structure is capable of performing a mechanical motion. An epitaxial layer covers at least a portion of the micromechanical structure. The micromechanical structure and the epitaxial layer are formed of different materials.
In preferred embodiments, the micromechanical structure and epitaxial layer are each preferably formed from a material selected from the group consisting of group IV, III-V, II-VI and IV-VI semiconductors. In particular, the micromechanical structure is preferably formed from a material selected from the group of solids consisting of Si, Ge, SiC, GaAs, InAs, InP GaP, GaSb, InSb, GaN, ZnO, CdTe and ZnTe. The epitaxial layer is preferably formed from a material selected from the group of solid solutions consisting of SiGeC, AlGaInPAsSb, AlGaInN and ZnCdHgOSSeTe. In one embodiment, the epitaxial layer is formed before the micromechanical structure is micromachined. In another embodiment, the epitaxial layer is formed on the micromechanical structure after the micromechanical structure is micromachined. The function of the epitaxial layer is dependent upon the material selected. In one embodiment, the epitaxial layer is formed of a material that provides a protective layer for the micromechanical structure. In another embodiment, the epitaxial layer is formed of a material that provides a measurable response to external stimulation of the micromechanical device. A secondary layer or layers of material may be formed on the epitaxial layer such that the epitaxial layer acts as an intermediate layer. Depending upon the application and the materials chosen, the micromechanical device may be a sensor, an actuator, an electronic device or an optoelectronic device.
The present invention also provides a micromechanical device including a single crystal micromachined micromechanical structure. At least a portion of the micromechanical structure is capable of performing a mechanical motion. An epitaxial layer is formed on at least a portion of the micromechanical structure after the micromechanical structure is micromachined.
In the present invention, since the micromechanical structure and the epitaxial layer are each preferably formed from a single crystal material, the resulting properties (mechanical, electronic, optical, etc.) of the micromechanical device are more readily reproduced employing known micromachining and thin film deposition techniques. In addition, single crystal materials which are stable at high temperatures and in harsh environments can be used. This allows the present invention micromechanical device to be used in a wider range of applications than is possible with devices having polycrystalline films which are susceptible to microstructure changes and preferential attack at grain boundaries. For example, with the appropriate selection of materials, devices of the present invention can operate with greater functionality at temperatures exceeding 1000xc2x0 C. as well as in environments found in gas turbines, internal combustion engines and munitions.